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I am going to be getting a 97 4x4 ext cab 5sp. with 113,000 miles. I am familiar with the cummins as I had a 24v. This truck has never been turned up. If I adust the starwheel and slide the fuel plate, and advancing the timing a little, and adjusting the valves on it, will I possibly pick up a little extra mpg? I already plan on putting on either a cold air intake or a high flow air filter and removing the cat/muffler and straight piping it out the back or putting stacks on it. I dont need huge power and drive with a very mild foot. Im out for a mpg rig. Any other ideas? Thanks!
 

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I am going to be getting a 97 4x4 ext cab 5sp. with 113,000 miles. I am familiar with the cummins as I had a 24v. This truck has never been turned up. If I adust the starwheel and slide the fuel plate, and advancing the timing a little, and adjusting the valves on it, will I possibly pick up a little extra mpg? I already plan on putting on either a cold air intake or a high flow air filter and removing the cat/muffler and straight piping it out the back or putting stacks on it. I dont need huge power and drive with a very mild foot. Im out for a mpg rig. Any other ideas? Thanks!
i did everything you just mentioned to mine and did see an increase in mileage, and i just replaced my overflow valve and got even better mileage as well and my tranny is slipping pretty good, so im sure you'll be able to get some good numbers and make sure you gotta fresh fuel filter on there as well.:thumbsup
 

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How does replacing your overflow valve help MPG?
 

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Discussion Starter #4
What do you mean by overflow valve?
 

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What do you mean by overflow valve?

Fuel return system



The fuel return system starts at the overflow valve that is on the engine side of
the injection pump even with the first delivery valve. The overflow valve looks
like a banjo fitting, but it contains a pressure valve. The type shown in the
picture has a spring, a steel ball, and a washer shaped like a tiny derby hat to
regulate pressure in the injection pump. This is essential so there will be adequate
fuel flow into the injection pump plungers when the fill ports open. The line from this
valve goes to the rubber return line discussed in “Fuel supply and return lines”
above. If there is low fuel pressure that is caused by a weak or defective overflow valve it is easy
to check. While the engine is running have someone watch the fuel pressure gauge. Clamp the
rubber return line closed with some pliers. If the low pressure is caused by this valve the pressure
read by the pressure gauge will increase very quickly. Do not hold the return line closed very
long to prevent damage to the fuel system. If the overflow valve is the cause and is the type
shown in the picture it may be temporarily repaired. Remove it from the injection pump. When
you do this cram a shop rag below the valve to catch any washers you may drop. If they get down
there you may never see them again. Take the entire valve off. Don’t remove the small screw
until you have the valve out and on your work bench. The spring in the overflow valve is
supposed to be a little bit longer then ½ inch, 0.550". If it is shorter you can stretch it a little. Just
a little bit goes a long ways. If you stretch it more than a little it will wreck the spring so it will be
worthless. The steel line from the overflow valve may crack and leak.
 

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How does replacing your overflow valve help MPG?
i honestly dont know the theory behind it that it would cause better mileage, im under the assumption that in order to have an efficient engine you need to have good fuel pressure and this is one way that fuel pressure is regulated, but it could be other things such as lift pump, fuel filter, fuel bowl(strainer), im sure someone else will give you more details, maybe even contradict what im saying...but take it for what its worth:thumbsup
 
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